CTLA4 and neoplasm: ICOS, known as a marker of T cell activation,30 is an essential costimulatory molecule for T cell enhancement.31, 32 Yi et al. have reported that T cells from peripheral blood and tumor tissues of patients treated with anti‐CTLA‐4 for NSCLC had an increased expression of ICOS.33 ICOS upregulation on T cells is correlated with increased clinical responses induced by CTLA‐4 inhibition.34, 35 Therefore, ICOS agonist mAbs could enhance the effect of inhibitory checkpoint inhibitors.